This invention relates to methods and apparatus for manufacturing such tubes as cans for preserved food are made from.
As for methods for manufacturing metal sheet tubes by means of butt welding, in U.S. Pat. No. 4,152,573 a method for manufacturing tubes is disclosed. As disclosed in that patent, two opposite edges of a sheet metal are held by a vise into abutting edge-to-edge engagement and such opposite edges are guided to pass through high energy zone of a laser beam and welded.
In U.S. Pat. No. 4,354,090, other prior art is disclosed.
As disclosed in that patent, two opposite edges of a sheet metal are guided in two guide channels of a Z-bar guide apparatus from radially offset position into intimate abutting edge-to-edge engagement with each other prior to introducing the sheet metal into a high energy welding apparatus such as a laser, electron beam or other welding machine. The method of holding two opposite edges of a sheet metal by a vise is disadvantageous in that circumferential positioning of abutting edges to a narrow energy focusing zone of a laser or the like requires a special device and apparatus for that method are complicated. That method is not fit for mass production because of batch processing.
The method of Z-bar guide apparatus is not fit for producing tubes of a large thickness to diameter ratio because distortion of a sheet metal is three-dimentional. And that process often causes defective welding at an edge of a seam because of bad abutting edge-to-edge relationship.
It is a primary object of this invention to provide a method for producing tubes by which abutting opposite edges of a sheet metal are accurately guided into high energy focusing zone of a welding machine such as a laser welder. It is further object of this invention to provide a method and an apparatus for producing tubes which is fit for mass production. It is another object of this invention to provide a method and an apparatus for producing tubes which is fit for production of tubes of a large thickness to diameter ratio.